Positive charge profiles in the silicon nitride film of MNOS device are investigated in conjunction with the distributions of electron traps and injected electrons which play the most important role on the write/erase operations as a nonvolatile memory. The results are: (1) the donor-like electron traps in the form of positive charges are uniformly distributed in the nitride bulk and the density is approximately 4 × 10 17 cm −3, (2) the injected electrons are trapped deeply into the nitride, where their depth depends on the magnitude of applied voltage to the gate, (3) the motion of positive charges retained for 50 days, is also measured, resulting in the diffusion coefficient of injected electrons of 10 −20 ∼ 10 −19 cm 2/sec.